Research On The Calculation And Characteristic Of Negative Friction Of Pile Foundation In Newly Thick Fill

With the rapid development of national economy, a large number of high-rise, super high-rise buildings have been emerged in city, the requirement of bearing capacityof foundation has been gradually improved, and whereas the pile foundation has beenwidely applied due to its high bearing capacity and small settlement, a lot of domestic and foreign scholars have carried out to study the bearing behavior of foundation largely. Because of the complexity of geological in different regions and special projectsite influence on pile foundation, some accidents have happened frequently, negative friction of pile is one of them. The building because of pile damaged and high settlement can not used due to negative friction being ignored in some pile foundation engineering, especially the newly filling soil, soft soil, collapsible loess geological, if the negative friction is ignored,it will be likely bring great economic losses. This article which adopts the method of theoretical calculation，static load test and numerical simulation, analyzes and researches the negative friction problem under newly deep fill.Firstly, this article explains the negative friction of pile whose the concept, the formation conditions, influence factors, the concept of neutral point and the method that can determine its position, and time effect, and sums up some common methods which can calculate the negative friction of pile. Potential loss of pile side soil and thetransfer of pile energy are considered by the methods above, therefore, based on theload transfer method, using Kezdi’s Double-Broken-Line model which can describe pileside friction load transfer,and Double line hardening model which is adopted to serveas load transfer of pile end. The model can be objectively reflected the pile load transfer characteristics of the soil by a large number of research. On this basis, accordingto conservation of energy, adopting double broken line type resistance on pile side and pile end energy method is to get the formula of the axial force and displacementand calculate the negative friction. the article which uses energy and calculates a typical project, verify the method, and it is shown that the this method is feasible in the calculation of negative frictionSecondly, aiming at the newly deep fill, combined a static load test the differencebetween vertical ultimate bearing capacity of single pile in static load test and one ofnormal use conditions is discussed. If negative friction is considered, the value of ultimate bearing capacity of single pile is1587KN,If not, it is2136,The value of static l oad is2000KN,the value is bigger than one that negative friction is not considered and smaller than one that negative friction is considered.The structure designer should consider the negative friction of pile,when bearing capacity of the pile foundation is used as a design standard, when testing the vertical ultimate bearing capacity of singlepile in static load test, the negative friction should not be considered by the structuredesigner，at the same time, the fill grouting reinforcement is advised in a certain rangearound pile in order to reduce the negative friction.Lastly, according to a project, by using FLAC3Dnumerical simulation, the different pile top load and heap load level in pile condition,which is simulated, impact onthe pile axial force and negative friction. Under the condition of allowance of the pilesettlement, increasing load on pile top appropriately can improve the bearing capacityof pile foundation, and the results and the method were compared and analyzed,the rationality of the theoretical calculation is verified.